Recently, as electronic devices have become more compact and multifunctional, and portable devices in particular have become lighter, thinner, and smaller, a circuit board used in the electronic devices has been required to have high density.
Thus, in order to increase the degree of integration of a circuit board within the same space, a multilayer circuit board, a circuit having flexibility to be installed in a narrow space, and a method of reducing the thickness of a metal layer for implementing a fine pattern on a circuit board have been used.
In particular, in the field of information processing and communication, in order to transfer and process large amounts of information at a high speed, the operating frequency of the CPU has been raised. An insulating layer having a low dielectric constant and excellent mechanical properties has been used so as to minimize a phenomenon in which signal propagation speed is delayed by the insulating layer.
A polyimide resin, which has excellent physical properties such as high heat resistance, dimensional stability, chemical resistance, and a relatively low dielectric constant, is widely used in electronic and electrical appliances such as for a circuit board and for insulating materials and parts where high reliability is required.
Typically, a polyimide resin is obtained by coating a polyamic acid on a substrate and heating the polyamic acid. But because the obtained polyimide resin generally has a dielectric constant of 3.0 or higher, the dielectric constant of the polyimide resin is required to be reduced so as to apply it to a field requiring a higher degree of integration and high-speed operation.
A polyamic acid and polyimide resin in various forms have been proposed, but methods that can be used while maintaining or improving the mechanical properties, to reduce the dielectric constant below a certain level, are not well known.
For example, a proposal to reduce polyimide π electrons to reduce the dielectric constant has been presented, but according to this, heat resistance of a polyimide resin is reduced and solder adhesion is broken. Further, the alicyclic unit has high solubility to an organic solvent, thus use of a produced film is limited, and the polyimide cannot have a sufficient dielectric constant for application for high speed operation and high circuit densities.
Thus, a polyimide resin having excellent mechanical properties with a low dielectric constant, that can minimize interference between signals, and that can greatly increase transfer speed is required.